Variation In Cd Accumulation Research Articles

Physiology and genetic architecture of traits associated with cadmium tolerance and accumulation in Populus nigra L.

Heavy metal tolerance and accumulation suggest that Populus nigra is suitable for phytoremediation. QTL mapping revealed the complex genetic architecture of cadmium response in this species and highlighted promising candidate genes. Poplar is promising for phytoremediation and a large phenotypic variation in response to Cd has been observed among and within Populus species. Scientific knowledge has increased regarding the physiological and molecular mechanisms of Cd response in poplars, however its genetic basis is still poorly understood. This study, investigated the genetic architecture of Cd accumulation and tolerance in Populus nigra L. A F1 progeny, grown in hydroponics under Cd treatment and control conditions, was analyzed by 21 phenotypic traits related to Cd tolerance, Cd accumulation, and chlorophyll fluorescence. These traits present a broad-sense heritability ranging from 0.22 to 0.57. Mapping of quantitative trait loci (QTL) revealed a total of 36 QTL for the female map and 21 QTL for the male map, corresponding to 12 and 11 genomic regions, respectively. The phenotypic variance explained by QTL ranged from 6.2 to 28.7 %, with an average of 14.5 %. Three main QTL cluster regions were defined on chromosomes IV and XIV. The projection of QTL intervals on the Populus trichocarpa Torr. & Gray annotated genome identified positional candidate genes (CGs), functionally related to the regulation of transcription, transport, response to oxidative stress, and the glutathione pathway. It was found that some CGs are directly related to Cd transport and detoxification, whereas other non-metal-specific CGs could also contribute to explain the phenotypic variation in Cd accumulation and tolerance. The high accumulation of Cd in roots and the relatively low translocation in leaves suggest that P. nigra would be a good candidate for the phytoremediation of metal-polluted sites.

Cadmium toxicity in Maize (Zea mays L.): consequences on antioxidative systems, reactive oxygen species and cadmium accumulation.

Increased cadmium (Cd) accumulation in soils has led to tremendous environmental problems, with pronounced effects on agricultural productivity. Present study investigated the effects of Cd stress imposed at various concentrations (0, 75, 150, 225, 300, 375 μM) on antioxidant activities, reactive oxygen species (ROS), Cd accumulation, and productivity of two maize (Zea mays L.) cultivars viz., Run Nong 35 and Wan Dan 13. Considerable variations in Cd accumulation and in behavior of antioxidants and ROS were observed under Cd stress in both maize cultivars, and such variations governed by Cd were concentration dependent. Exposure of plant to Cd stress considerably increased Cd concentration in all plant parts particularly in roots. Wan Dan 13 accumulated relatively higher Cd in root, stem, and leaves than Run Nong 35; however, in seeds, Run Nong 35 recorded higher Cd accumulation. All the Cd toxicity levels starting from 75 μM enhanced H2O2 and MDA concentrations and triggered electrolyte leakage in leaves of both cultivars, and such an increment was more in Run Nong 35. The ROS were scavenged by the enhanced activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and glutathione peroxidase in response to Cd stress, and these antioxidant activities were higher in Wan Dan 13 compared with Run Nong 35 at all Cd toxicity levels. The grain yield of maize was considerably reduced particularly for Run Nong 35 under different Cd toxicity levels as compared with control. The Wan Dan 13 was better able to alleviate Cd-induced oxidative damage which was attributed to more Cd accumulation in roots and higher antioxidant activities in this cultivar, suggesting that manipulation of these antioxidants and enhancing Cd accumulation in roots may lead to improvement in Cd stress tolerance.

Genome-wide association mapping of cadmium accumulation in different organs of barley.

The threshold value of cadmium (Cd) concentration in grains of barley (Hordeum vulgare) is the lowest among cereal crops; however, it is poorly understood how Cd accumulation in barley grain is genetically controlled. We investigated genotypic variation in Cd accumulation of different organs in 100 accessions from a subset of the barley core collection using both hydroponic and Cd-contaminated soil culture. We also performed a genome-wide association (GWA) mapping for Cd accumulation in different organs. A large genotypic variation in the Cd concentration was found in all organs. There was a good correlation between shoot Cd of solution and soil culture, the shoot Cd and grain Cd, but no correlation between the root Cd and grain Cd. GWA mapping detected 9 quantitative trait loci (QTL) for root Cd, 21 for shoot Cd, 14 for root-to-shoot translocation and 15 for grain Cd. A common QTL for the shoot Cd and root-to-shoot translocation was found at 132.6 cM on chromosome 5H. Two major QTL for grain Cd were identified on chromosome 2H and chromosome 5H. The genetic variation in Cd accumulation and major QTL detected provide useful information helpful for cloning candidate genes for Cd accumulation and breeding low-Cd barley cultivars in future.

Identification of quantitative trait loci for cadmium accumulation and distribution in rice (Oryza sativa)

Cadmium (Cd) poses a serious risk to human health due to its biological concentration through the food chain. To date, information on genetic and molecular mechanisms of Cd accumulation and distribution in rice remains to be elucidated. We developed an independent F7 RIL population derived from a cross between two japonica cultivars with contrasting Cd levels, 'Suwon490' and 'SNU-SG1', for QTLs identification of Cd accumulation and distribution. 'Suwon490' accumulated five times higher Cd in grain than 'SNU-SG1'. Large genotypic variations in Cd accumulation (17-fold) and concentration (12-fold) in grain were found among RILs. Significant positive correlations between Cd accumulation in grain with shoot Cd accumulation and shoot to grain distribution ratio of Cd signify that both shoot Cd accumulation and shoot to grain Cd distribution regulate Cd accumulation in japonica rice grain. A total of five main effect QTLs (scc10 for shoot Cd accumulation; gcc3, gcc9, gcc11 for grain Cd accumulation; and sgr5 for shoot to grain distribution ratio) were detected in chromosomes 10, 3, 9, 11, and 5, respectively. Of these, the novel potential QTL sgr5 has the strongest effect on shoot to grain Cd distribution. In addition, two digenic epistatic interaction QTLs were identified, suggesting the substantial contribution of nonallelic genes in genetic control of these Cd-related traits.

Cultivar variation in morphological response of peanut roots to cadmium stress and its relation to cadmium accumulation

This study aimed to test the hypothesis that root morphology may play a crucial role in the variation in Cd accumulation among peanut (Arachis hypogaea L.) cultivars. The biomass, Cd accumulation and root morphology of five peanut cultivars were determined under 2 and 20μM CdCl2 in a hydroponic experiment. Excess Cd considerably decreased the root lengths (RL), surface area (SA), specific root length (SRL) and number of root tips, but increased the root diameters (RD). Cd-induced decreases in RL and SA were significant in the 0–0.2 and 0.2–0.4mm diameter classes. Peanut cultivars differ in Cd accumulation and root morphological parameters. A positive correlation was observed between RL and Cd amount in shoots. RD negatively correlated to Cd concentrations in roots and shoots. Positive correlations were also found between RL vs. shoot Cd concentration, SA vs. Cd amount in shoots, SRL vs. root Cd concentration, SRL vs. shoot Cd concentration, and SRL vs. Cd amount in shoots. The fine roots play a crucial role in determining Cd accumulation in peanut plants. Cultivars with more fine roots in their root system (i.e. Haihua 1 and Zhenghong 3) have high capability of Cd accumulation.

Genome-Wide Association Studies Identify Heavy Metal ATPase3 as the Primary Determinant of Natural Variation in Leaf Cadmium in Arabidopsis thaliana

Understanding the mechanism of cadmium (Cd) accumulation in plants is important to help reduce its potential toxicity to both plants and humans through dietary and environmental exposure. Here, we report on a study to uncover the genetic basis underlying natural variation in Cd accumulation in a world-wide collection of 349 wild collected Arabidopsis thaliana accessions. We identified a 4-fold variation (0.5–2 µg Cd g−1 dry weight) in leaf Cd accumulation when these accessions were grown in a controlled common garden. By combining genome-wide association mapping, linkage mapping in an experimental F2 population, and transgenic complementation, we reveal that HMA3 is the sole major locus responsible for the variation in leaf Cd accumulation we observe in this diverse population of A. thaliana accessions. Analysis of the predicted amino acid sequence of HMA3 from 149 A. thaliana accessions reveals the existence of 10 major natural protein haplotypes. Association of these haplotypes with leaf Cd accumulation and genetics complementation experiments indicate that 5 of these haplotypes are active and 5 are inactive, and that elevated leaf Cd accumulation is associated with the reduced function of HMA3 caused by a nonsense mutation and polymorphisms that change two specific amino acids.

Genotype variations in accumulation of cadmium and lead in celery (Apium graveolens L.) and screening for low Cd and Pb accumulative cultivars

To help reduce risks of heavy metal pollution, two pot experiments were conducted to investigate the variations, transfer potential, and stability of Cadmium (Cd) and Lead (Pb) accumulations in celery (Apium graveolens L.) and to screen for low Cd and Pb accumulative cultivars. The maximum differences in shoot Cd concentration were 4.7-fold under low-Cd exposure and 3.3-fold under high-Cd exposure. These genotype variations in Cd accumulation are sufficiently large to help reduce Cd contamination risk in soil by using the Low-Cd-Accumulative genotypes. Cd accumulation of the Low-Cd-Accumulative genotypes is significantly positive correlated with Pb accumulation. Evidence obtained proves that Cd and Pb accumulations in celery are stable and genotype-dependent at the cultivar level. The presence of high-Pb contamination in soil promoted Cd accumulation in shoots of celery. Celery is considered a species with high risks in Cd pollution and low risks in Pb pollution. Among the tested cultivars, cv. Shuanggangkangbing (SGKB) had the lowest shoot Cd and Pb accumulating abilities, and thus is the most important material for breeding of pollution-safe cultivars (PSCs) to minimize Cd and Pb accumulations in celery.

Responses of Different Chinese Flowering Cabbage (Brassica parachinensis L.) Cultivars to Cadmium and Lead Exposure: Screening for Cd + Pb Pollution‐Safe Cultivars

AbstractTo reduce the potential risks of cadmium (Cd) and lead (Pb) entering the human food chain in vegetables, two pot experiments (Exp. 1 and Exp. 2) were carried out to screen for Cd and Pb pollution‐safe cultivars (PSCs) of Chinese flowering cabbage (Brassica parachinensis L.). The three Cd treatments in Exp. 1 (0.114, 0.667, and 1.127 mg kg−1) showed that Chinese flowering cabbage could easily take up Cd from polluted soils, and there were wide variations in Cd accumulation among different cultivars. The Cd accumulation trait at cultivar level was rather stable under different soil Cd treatments. In Exp. 2, seven cultivars that had been shown in Exp. 1 to be typical high or low accumulators of Cd were selected and six Cd + Pb joint exposure treatments were applied to them. The results showed that there were similar trends of accumulation between Cd and Pb for the tested cultivars, but Pb accumulation by the species was much poorer than that of Cd. It was worth noting that an increase in soil Pb levels significantly (p < 0.01) depressed shoot Cd accumulation. Six cultivars were selected as Cd + Pb PSCs. This study showed that it is feasible to apply a PSC strategy in Chinese flowering cabbage cultivation, to cope with the Cd and Pb contamination commonly found in agricultural soils.

Accumulation of cadmium by flax and linseed cultivars in field-simulated conditions: A potential for phytoremediation of Cd-contaminated soils

The possibility of use of two technological types of Linum usitatissimum L., namely flax (grown for fibre) and linseed (grown for seed), for phytoextraction of cadmium (Cd) from Cd-contaminated soil was studied. A four-year field-simulated experiment was carried out with 6 flax and 4 linseed cultivars in order to study organ accumulation of Cd by flax and linseed plants at artificial concentration range 10–1000 mg Cd kg −1 soil. The most Cd was accumulated by roots, followed by shoots, while reproductive parts (capsules and seeds) played comparably smaller role. The increasing soil Cd concentration resulted in increasing Cd accumulation by roots, while transport to above-ground plant parts was progresivelly inhibited. Even high soil Cd concentrations (1000 mg Cd kg −1 soil) had not dramatic negative effect on plant growth and development. Cultivar differences as well as the differences between both technological Linum types have been found in Cd accumulation (flax being better Cd accumulator than linseed). Nevertheless, the recorded variation between technological types and within cultivars is in multiples of Cd values (units of mg Cd kg −1 DW), not in orders of magnitude as needed for practical phytoextraction. A significant year-to-year effect on plant growth/development resulting in high variation in Cd accumulation was observed. Flax cv. Jitka exhibited good transport of Cd from roots to above-ground parts, while flax cv. Merkur showed high retention of Cd in roots. Further, the contrasting cultivars in total Cd accumulation (high accumulating flax cv. Jitka versus low accumulating linseed cv. Jupiter) were selected for future experiments. The uptake of Cd by flax/ linseed from ha per season was calculated and the strategy for flax/linseed growing on heavy metal polluted soils with subsequent utilization of heavy metal-contaminated biomass is discussed.

Genotypic variation of cadmium accumulation and distribution in rice

An effective way to reduce the risk of cadmium (Cd) entering the food chain is to use low Cd-accumulation rice cultivars, particularly in Asia. The fundamental requirement for breeding low grain Cd-accumulation cultivars is to know the genotypic variation in Cd accumulation and the physiological processes and genetic basis governing the Cd accumulation in rice grain. In this experiment, genotypic variation in Cd accumulation and distribution among rice organs was studied using thirty-five rice varieties. They were grown with irrigation water containing 2 ppm Cd throughout rice growing season under field condition in 2007. At harvest, plants were sampled and analyzed for Cd concentration and accumulation in each rice organ. Significant variation of Cd concentration and accumulation in rice organs were found among thirty-five rice cultivars, revealing more than 8-fold varietal differences in grain Cd concentration and shoot Cd accumulation. Cd concentration and accumulation in grain were significantly different among cultivar groups, showing the highest in indica and the lowest in temperate japonica. Tongil-type and tropical japonica rice showed a Cd concentration intermediate to that of temperate japonica and indica rice. The higher Cd accumulation in grain of indica rice was attributable to the greater ability of Cd uptake. The greater ability of root-shoot translocation in tropical japonica and shoot-grain redistribution in tongil-type resulted in the significantly higher grain Cd concentration in these cultivar groups than in temperate japonica. For over 35 cultivars tested, grain Cd concentration revealed a significant positive correlation with root Cd concentration and shoot Cd concentration and accumulation while no significant correlation with root-shoot translocation factor and shoot-grain redistribution ratio. However, correlation analyses within each cultivar group showed that grain Cd concentration was significantly correlated with root-shoot translocation factor in indica, with root Cd concentration in tongil-type, with shoot Cd concentration and accumulation in tropical japonica, and with shoot Cd accumulation and shoot-grain redistribution ratio in temperate japonica. These results indicate that genotypic variation in grain Cd accumulation, in general, is controlled by all the three physiological processes but the major physiological process governing its genotypic variation within cultivar group is different depending on cultivar groups.

A major quantitative trait locus controlling cadmium translocation in rice (Oryza sativa)

The trait of low cadmium (Cd) accumulation in brown rice (Oryza sativa) is important for food safety. An effective way to reduce Cd accumulation in the grain is to control Cd transfer from the roots to the shoots. Here, we investigated genotypic variation in the shoot Cd concentration among 146 accessions from a rice core collection and performed a quantitative trait locus (QTL) analysis to determine the loci controlling shoot Cd accumulation. Furthermore, we physiologically characterized the two accessions used for QTL analysis. Large genotypic variation (13-fold) in the shoot Cd concentration was found. A major QTL was detected on chromosome 11 using a F2 population derived from Badari Dhan (a high-Cd accession) and Shwe War (a low-Cd accession). This QTL explained 16.1% of the phenotypic variation in Cd accumulation. Furthermore, this QTL was confirmed by analysis of advanced progeny. Physiological studies showed that Badari Dhan and Shwe War did not differ in uptake of Cd by the roots, but differed greatly in the translocation of Cd from the roots to the shoots. Taken together, our findings suggest that the major QTL detected is responsible for the translocation of Cd from the roots to the shoots.

Cd accumulation in roots and shoots of durum wheat: the roles of transpiration rate and apoplastic bypass

Cadmium is readily taken up from soils by plants, depending on soil chemistry, and variably among species and cultivars; altered transpiration and xylem transport and/or translocation in the phloem could cause this variation in Cd accumulation, some degree of which is heritable. Using Triticum turgidum var. durum cvs Kyle and Arcola (high and low grain Cd accumulating, respectively), the objectives of this study were to determine if low-concentration Cd exposure alters transpiration, to relate transpiration to accumulation of Cd in roots and shoots at several life stages, and to evaluate the role of apoplastic bypass in the accumulation of Cd in shoots. The low abundance isotope (106)Cd was used to probe Cd translocation in plants which had been exposed to elemental Cd or were Cd-naïve; apoplastic bypass was monitored using the fluorescent dye PTS (8-hydroxy-1,3,6-pyrenetrisulphonate). Differential accumulation of Cd by 'Kyle' and 'Arcola' could be partially attributed to the effect of Cd on transpiration, as exposure to low concentrations of Cd increased mass flow and concomitant Cd accumulation in 'Kyle'. Distinct from this, exposure of 'Arcola' to low concentrations of Cd reduced translocation of Cd from roots to shoots relative to root accumulation of Cd. It is possible, but not tested here, that sequestration mechanisms (such as phytochelatin production, as demonstrated by others) are the genetically controlled difference between these two cultivars that results in differential Cd accumulation. These results also suggest that apoplastic bypass was not a major pathway of Cd transport from the root to the shoot in these plants, and that most of the shoot Cd resulted from uptake into the stele of the root via the symplastic pathway.

Genotypic variation in cadmium accumulation by seed of linseed, and comparison with seeds of some other crop species

The accumulation of cadmium (Cd) in plants is a health issue because a range of grain and vegetable crops can accumulate levels of Cd that are in excess of limits set by the World Health Organization and individual countries. Many Australian agricultural soils used to produce confectionery linseed have a history of intensive use of Cd-contaminated phosphatic fertilisers and this, combined with soil properties such as high chloride salinity, can result in enhanced availability of Cd to crops. We investigated genotypic variation in Cd accumulation in seed of 17 linseed and Linola (termed linseed) lines from Australia and elsewhere in a glasshouse study using a soil from southern Australia that had a history of the application of Cd-contaminated phosphatic fertiliser. Canola, Indian mustard, lupins, and wheat were also included in the study for comparison. Under the experimental conditions, Cd concentrations in seed of all but one of the linseed lines exceeded the maximum permitted concentration (MPC) of 250 µg/kg for confectionery linseed traded on the international market. There was a 2.3-fold variation in seed Cd concentrations between all the linseed lines (range, 233–545 µg/kg). Linseed lines from Australia and overseas were equally capable of accumulating Cd in seed. Brown-seeded and golden-seeded lines accumulated similar concentrations of Cd. Canola, Indian mustard, lupins, and wheat accumulated about 10-fold lower concentrations of Cd in seed than linseed, and did not exceed Australian or other MPCs. There was little difference in Cd concentrations between the seed and de-seeded capsules of linseed, but a large difference in Cd concentration between the seed and de-seeded fruit parts of the other crops. The mean seed to de-seeded fruit part Cd concentration ratio for linseed was 0.87 : 1 compared with a ratio of 0.35 : 1 for the other crops, suggesting that linseed has comparatively ineffective barriers discriminating against the transport of Cd to seed. Analysis of seed lots of confectionery linseed sampled from a grain receival depot showed that seed lots from farms in Victoria (range 140–560 µg Cd/kg) had 5-fold greater Cd concentrations than those from farms in New South Wales (range 20–160 µg/kg). This is presumably due to a more intensive history of the application of Cd-contaminated phosphatic fertiliser to pastures and crops in Victoria, as well as differences in environmental and soil conditions.

Effects of soil properties and cultivar on cadmium accumulation in wheat grain

AbstractCd accumulation in the grain of wheat cultivars grown on soils at seven experimental sites in the Austrian wheat zone was significantly affected by soil chemical characteristics and by cultivar. Multiple linear regression analyses indicate that about 80% of the variation in Cd accumulation may be explained by cultivar. total soil Cd, and organic carbon (OC). An additional 10% of the variation was correlated with Cl− and Ca2+ in the soil solution. Uptake of Cd increased with higher soil Cd content and higher Cl− concentrations in soil solution, but decreased at higher levels of OC and soluble Ca. Cd accumulation varied by a factor of up to 2.5 among cultivars. The highest Cd accumulation was found in some spring durum cultivars in soils containing relatively low total Cd (< 0.4 mg kg−1); at some sites the maximum permissible Cd concentrations in wheat grain (0.1 mg kg−1) was exceeded according to German regulations. Selecting low Cd‐accumulating cultivars and adjusting soil chemical conditions may provide alternatives to reduce Cd intake in human diet.

Variation in Cadmium Accumulation Potential and Tissue Distribution of Cadmium in Tobacco

Variation in Cd accumulation between Nicotiana species but not varieties has been observed in seedlings grown in solution culture with moderate-to-low levels of Cd. Nicotiana tabacum has been characterized as a leaf and root accumulator while Nicotiana rustica is shown to be primarily a root accumulator, having about half the leaf Cd per gram dry weight of N. tabacum. This phenotype is retained in the mature N. rustica plant. To characterize these two species which differ in their modes of Cd accumulation, tissue Cd distribution, partitioning of metal in soluble and insoluble fractions and the contribution of soluble Cd-binding proteins (peptides) to total plant Cd was assessed using mature solution cultured plants. Metal accumulation was highest in the most mature leaves and in young roots. The preponderance of young roots in N. rustica may, in part, account for low leaf/high root Cd accumulation in this species. While Cd-binding peptides appear to be a principal form of Cd in leaves and roots of seedlings and these also occur in mature leaves, Cd is equally distributed between soluble (about 80% as Cd-binding peptide) and uncharacterized insoluble forms in mature plant roots.